278 



MESSRS. A. IIAKKEK AND J. E. MARK ON 



products rather than original inclusions *. They are well seen in 

 the blade-like micas already referred to. 



Mr. J. A. Phillips mentioned hornblende as a constituent of the 

 Shap granite, but it is not found in any of our numerous specimens 

 and slices. 



The felspars of our rock fall under three heads : the earlier ortho- 

 clase, the plagioclase, and the later orthoclase. The first builds the 

 large red crystals which give to the rock its porphyritic appearance. 

 The crystals show the common habit, and are usuallj* twinned on 

 the Carlsbad law. The mineral is clearly monoclinic. Mr. Phillips 

 speaks of it in one place as " microcline," but as the specimens 

 aUuded to formed part of the facade of a building, it is clear that 

 they could not have been subjected to any decisive test. These large 

 felspars enclose crystals of apatite and spheiie, besides occasional 

 flakes of mica and prisms of striated plagioclase. More rarely they 

 contain little patches of quartz, or even a well-bounded crystal of 

 that mineral [395]. Sometimes, however, we find numerous round 

 grains of quartz enclosed in the marginal portion of the felspar 

 crystals [796]. The inference is that these porphyritic crystals were 

 formed at a time when the accessory constituents of the rock had 

 already separated out, and the mica and plagioclase had begun to 

 form, and that their growth only occasionally continued into the 

 stage at which free silica began to separate. 



For the following analysis (I.) of the porphyritic felspars we are 

 indebted to the kindness of Dr. J. B. Cohen. The figures are the 

 mean of two determinations : — 





I. 



II. 



III. 



SiO, ... 



05-41 



64-48 



68-89 



A1P3 . . 



18-97 



19-04 



15-48 



^ 



Pe,03 . . . 



. . 



. . 



2-46 



FeO ... 



0-51 



, . 



traces 



MnO . . . 



traces 



, , 



0-58 



MgO . . . 



0-Ul 



1-02 



1-04 



CaO .. 



0-73 



, , 



2-13 



Na,0 . . . 



2-15 



2-64 



4-69 



K,() ... 



11-23 



10-74 



3-70 



H.,0 ... 



. not estim. 



0-78 (ign.) 



not estim 



99-01 



98-70 



98-97 



I. Porphyritic pink felspar of the Shap Pell granite : anal. J. B. 



Cohen. 

 II. Dominant felspar of the granite of Glenmalure, Co. Wicklow : 

 anal. Galbraith -. cit. Haughton, Quart. Journ. Geol. Soe. 

 vol. xii. (1856) p. 173. 

 III. Groundmass of the Shap Fell granite : anal. J. B. Cohen. 



The percentage of soda is worthy of notice ; a small part of it is 



* Eosenbiisch, ' Mikr. Pln>iogr. d. petr. wichtig. Miner.' 2nd ed. (1885) 

 p. 303. See also \V. Maynard Ilutchings, Geol. Mag. (1890) p. 264. 



